list1210.cpp

teach yourself C++ in 21 days 第五版

//Listing 12.10 Data slicing with passing by value
#include <iostream>
using namespace std;
 
class Mammal
{
  public:
     Mammal():itsAge(1) {  }
     virtual ~Mammal() { }
     virtual void Speak() const { cout << "Mammal speak!\n"; }
   
  protected:
     int itsAge;
};

class Dog : public Mammal
{
  public:
    void Speak()const { cout << "Woof!\n"; }
};

class Cat : public Mammal
{
  public:
    void Speak()const { cout << "Meow!\n"; }
};

void ValueFunction (Mammal);
void PtrFunction (Mammal*);
void RefFunction (Mammal&);
int main()
{
   Mammal* ptr=0;
   int choice;
   while (1)
   {
      bool fQuit = false;
      cout << "(1)dog (2)cat (0)Quit: ";
      cin >> choice;
      switch (choice)
      {
        case 0: fQuit = true;
                break;
        case 1: ptr = new Dog;
                break;
        case 2: ptr = new Cat;
                break;
        default: ptr = new Mammal;
                 break;
      }
      if (fQuit==true)
         break;

      PtrFunction(ptr);
      RefFunction(*ptr);
      ValueFunction(*ptr);
   }
   return 0;
}

void ValueFunction (Mammal MammalValue)
{
   MammalValue.Speak();
}

void PtrFunction (Mammal * pMammal)
{
   pMammal->Speak();
}

void RefFunction (Mammal & rMammal)
{
   rMammal.Speak();
}